Flat tube and heat exchanger

ABSTRACT

A flat tube for a heat exchanger has a tube body with an outer top and an outer bottom surface arranged opposite one another at a thickness of the tube body and two outer side surfaces arranged opposite one another at a width of the tube body and connecting the outer top and bottom surfaces. The tube body has a heat exchange portion extending along an extension direction, an angled portion extending along an transverse direction inclined relative to the extension direction, and a bent portion connecting the heat exchange portion to the angled portion. The angled portion is arranged at a distance from the heat exchange portion in an offset direction. The bent portion has a first end region facing the heat exchange portion with a first bend counter to the offset direction and a second end region facing the angled portion with a second bend in the offset direction.

TECHNICAL FIELD

The invention relates to a flat tube for a heat exchanger as well as to a heat exchanger having such flat tubes.

BACKGROUND

In heat pump applications and heat exchangers having exclusively one single passage it is a problem that under unfavorable environment conditions the single passage may freeze up easily. This problem could be solved in that, for example, a refrigerant pressure drop in a heat exchanger block having flat tubes is increased, e.g. by an increased deflection of the refrigerant in the heat exchanger block. An increase of the pressure drop goes hand in hand with increasing a boiling temperature of the refrigerant as a result of which the temperature of the flat tubes or of the heat exchanger block can be increased and thus the risk of a freezing can be at least reduced. This can be achieved for example by a meander-like or multi-loop flow through the heat exchanger.

From CN 103 644 685 A, a heat exchanger having two inflow collectors and two outflow collectors is known. This heat exchanger has two types of flat tubes stacked upon one another alternatingly. The flat tubes of a second type are substantially straight. The flat tubes of first type have a sharp bend or fold near their longitudinal ends, in which bend or fold a central heat exchange portion of the respective flat tubes merges into an angled portion of these flat tubes. Accordingly, a first of the inflow and a first of the outflow collectors are arranged in line with flat tubes of the second type and a second of the inflow and a second of the outflow collectors are each arranged aside of the flat tubes of the second type and connected to the angled portions of the flat tubes of the first type.

However, the sharp bend or fold near the longitudinal ends of the flat tubes (of the first type) leads to increased internal mechanical stresses in the area of the sharp bend or fold. Thus, such usual flat tubes may be prone to material failure either during their manufacturing or whilst operation of the heat exchanger due to the coolant or refrigerant pressure they have to withstand when the heat exchanger is operated.

SUMMARY

The present disclosure presents new ways for the development of flat tubes for heat exchangers.

A general idea of the invention therefore is to configure the bent portion of the flat tube for a heat exchanger as to have a first and a second bend, via which a heat exchange portion of the flat tube merges into an angled portion of the flat tube.

Advantageously, this results in an increased bending radius opposite that of usual bent flat tubes and thus allows for improved strength of the flat tube and less likely failure during its manufacturing or operation.

The invention concerns a flat tube for a heat exchanger, having a tube body delimiting at least one coolant channel through which a coolant or a refrigerant can flow. The tube body has an outer top and an outer bottom surface arranged opposite one another at a thickness of the tube body as well as two outer side surfaces arranged opposite one another at a width of the tube body, the outer side surfaces connecting the outer top to the outer bottom surface. It goes without saying that the expressions “outer top surface” and “outer bottom surface” only refer to a preferred orientation of the flat tube, wherein this orientation can be deviated from without leaving the scope of the invention. Thus, if practical, the flat tube in its operation position can be orientated as to have its outer bottom surface facing upwards or downwards or sideways with respect to gravity. The tube body has a heat exchange portion substantially extending along an extension direction. The tube body has an angled portion substantially extending along a transverse direction that is inclined with respect to the extension direction. Preferably, the first bend has an S- or Z-like shape comprising two sub-bends, one of which is directed against and one of which is directed in the offset direction, wherein both sub bends together cause the tube body to withdraw counter to the offset direction whilst distancing from the heat exchange portion in the extension direction. The tube body also has a bent portion connecting the heat exchange portion to the angled portion. The angled portion is arranged at a distance from the heat exchange portion measured in an offset direction substantially perpendicular to both the extension and the transverse direction. The bent portion in its first end region facing the heat exchange portion has a first bend counter to the offset direction. In its second end region facing the angled portion, the bent portion has a second bend in the offset direction. This allows for a particular big bending radius of the bent portion, such that the mechanical strength of the flat tube can be enhanced and its manufacturing can be simplified.

According to a preferred embodiment of the flat tube, the second bend is a twist-bend. By that, both the inclination of the angled portion opposite the heat exchange portion and the distance between the angled portion and the heat exchange portion along the offset direction can be achieved in a single and thus inexpensive deformation process.

According to another preferred embodiment of the flat tube, the extension direction substantially follows a straight line. This allows for particular effective heat exchange.

In another preferred embodiment of the flat tube, the transverse direction is substantially perpendicular to the extension direction. Such a flat tube is particularly cost-effective to produce.

In another preferred embodiment of the flat tube, the distance at which the angled portion is arranged opposite the heat exchange portion is smaller than a minimum bending radius of the second bend. This way, a mechanical load when bending the flat tube to its final shape whilst manufacturing can be kept below a failure load.

According to another preferred embodiment of the flat tube, the minimum bending radius of the second bend is 3 to 6 times the tube thickness. This ratio of the bending radius of the second bend to the tube thickness has proven to be particularly suitable. In addition or as an alternative, the minimum bending radius of the second bend is 0.70 to 0.95 times the tube width. In addition or as an alternative, heat transfer fins can be present at the outer top and/or bottom surface, wherein the heat fins protrude from the respective outer top and/or bottom surface along a fin height, which fin height is measured perpendicularly opposite the respective outer top and/or bottom surface, the minimum bending radius of the second bend being 0.70 to 0.95 times the fin height.

According to another preferred embodiment of the flat tube, the tube body delimits numerous coolant channels arranged in a queue along the width of the tube, wherein between directly adjacent coolant channels a division wall extending along the thickness of the tube body is present. Such a flat tube allows for particularly even heat exchange distribution at its outer upper and bottom surfaces. Furthermore, such flat tubes can have a particularly small thickness.

In another preferred embodiment of the flat tube, the tube body has a uniform material or consists of a uniform material, which material preferably is a metal. This enhances the heat transfer/exchange and allows bending a semi-finished straight flat tube as to match the geometry of the flat tube according to this embodiment of the invention.

According to another preferred embodiment of the flat tube, the bent portion in a view perpendicular both to the extension and to the offset direction has an S- or Z-like geometry. This means that if the first bend comprises two sub-bends, which together form an S- or Z-like shape, the second bend steadily adds to the S- or Z-like shape as to form the S- or Z-like geometry of the bent portion. By that, the bending radius of the second bend can be increased.

The invention also relates to a heat exchanger, which has first flat tubes, which accord to the invention as described above, wherein longitudinal ends of their angled portions facing away from their bent portions are received in associated second openings of a second collector. Thus, the afore-mentioned advantages of the flat tube according to the invention transfer to the heat exchanger, accordingly. Furthermore, the heat exchanger has second flat tubes, wherein first longitudinal ends of these second flat tubes are received in associated third openings of a third collector and second longitudinal ends of the second flat tubes, which are arranged opposite their first longitudinal ends, are received in associated fourth openings of the first collector. The first and fourth openings are arranged spaced apart from one another.

According to a preferred embodiment of the heat exchanger, the first flat tubes and the second flat tubes are arranged alternatingly along a stacking direction that corresponds to, in particular equals, the offset direction of the first flat tubes. By the alternating arrangement of the individual flat tubes a defrosting capacity can be increased. Thereby, a defrosting cycle can be shortened and the overall energy efficiency of the heat exchanger can be increased.

In another preferred embodiment of the heat exchanger, an intermediate space is present between adjacent flat tubes, in which heat transfer fins are accommodated. This enhances the heat exchange/transfer between a fluid led through the intermediate space and the coolant or refrigerant flowing through the flat tubes, since the heat transfer fins effectively increase a heat exchange surface area of the heat exchanger.

Preferably, whilst assembling the heat exchanger, the heat transfer fins are held in place by the first bend.

According to another preferred embodiment of the heat exchanger, in a view along the stacking direction the heat exchange portions of the first flat tubes completely overlap the second flat tubes, whereas the angled portions of the first flat tubes do not. This allows for particularly well heat exchange whilst keeping a profile of the heat exchanger and an air pressure drop low.

In another preferred embodiment of the heat exchanger, the second flat tubes are substantially straight. Such second flat tubes can easily be taken from stock without any manufacturing or modification process on them to be carried out but cutting to length.

According to another preferred embodiment of the heat exchanger, the second flat tubes as well as the first flat tubes accord to the invention as described above. Then, the transverse direction of the first flat tubes differs from that of the second flat tubes. Such a heat exchanger can be set up in a particular compact design.

Further important features and advantages of the invention become evident from the drawings and from the associated detailed description by way of the drawings.

It is to be understood that the features mentioned above and still to be explained in the following cannot only be used in the respective combination stated but also in other combinations or by themselves without leaving the scope of the present invention.

Preferred exemplary embodiments of the invention are shown in the drawings and are explained in more detail in the following description, wherein same reference numbers relate to same or similar or functionally same components.

BRIEF DESCRIPTION OF THE DRAWINGS

It shows, in each case schematically:

FIG. 1A shows an example of a flat tube according to the invention in a view against a transverse direction;

FIG. 1B shows the example of FIG. 1A in a view along an offset direction;

FIG. 2A shows another example of the flat tube according to the invention in a view along the offset direction;

FIG. 2B shows the example of FIG. 2A in a view opposite the transverse direction;

FIG. 3A shows, partially, an example of a heat exchanger according to the invention in a view against the transverse direction;

FIG. 3B shows a first flat tube of the heat exchanger of FIG. 3A in a view along the offset direction;

FIG. 4A shows the heat exchanger of FIG. 3A in a plan view along the offset direction; and

FIG. 4B shows another example of the heat exchanger according to the invention in a plan view along the offset direction.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1A shows an example of a flat tube 1 according to the invention in a view against a transverse direction 10, which flat tube 1 is configured to be implemented in a heat exchanger 30 according to the invention, the latter being depicted in FIGS. 3A, 4A and 4B and described later on. FIG. 1B shows the example of FIG. 1A in a view along an offset direction 12. As to be seen from FIGS. 1A and 1B, the flat tube 1 has a tube body 2, which delimits at least one coolant channel 3 through which a coolant or a refrigerant can flow. In the example of FIG. 1A, the tube body 2 delimits numerous coolant channels 3, which are arranged in a queue along the width W of the tube 1. A division wall 17 extending along the thickness T of the tube body 2 is present between two directly adjacent coolant channels 3. For example, tube body 2 has a uniform material or consists of such a uniform material. The material of the tube body 2 for instance is a metal.

FIG. 2A illustrates another example of the flat tube 1 according to the invention in a view along the offset direction 12. FIG. 2B shows the example of FIG. 2A in a view against the transverse direction 10. In other words, the perspective of FIG. 2A corresponds to that of FIG. 1B, whereas the perspective of FIG. 2B is similar to that of FIG. 1A. For the sake of clarity and better understanding, the coolant channels 3 of the tube body 2 are not shown in the example of FIGS. 2A and 2B.

As to be seen from FIGS. 1A, 1B, 2A and 2B, the tube body 2 has an outer top surface 4 and an outer bottom surface 5, which are arranged opposite one another at a thickness T of the tube body 2. Tube body 2 also has two outer side surfaces 6, which are arranged opposite one another at a width W of the tube body 2. The outer side surfaces 6 connect the outer top and the outer bottom surface 4, 5. Tube body 2 has a heat exchange portion 7, which substantially extends along an extension direction 8. Tube body 2 has an angled portion 9, which substantially extends along a transverse direction 10 that is inclined with respect to the extension direction 8. Tube body 2 has a bent portion 11, which connects the heat exchange portion 7 to the angled portion 9.

It is to be seen from FIGS. 1A and 2B, that the angled portion 9 is arranged at a distance D from the heat exchange portion 7, which distance D is to be measured in the offset direction 12. The offset direction 12 is substantially perpendicular to both the extension and the transverse direction 8, 10. The bent portion 11 has a first bend 14, which is present in a first end region 13 of the bent portion 11 that faces the heat exchange portion 7. The first bend 14 of the bent portion 11 is bent counter to the offset direction 12. Furthermore, the bent portion 11 has a second bend 16, which is present in a second end region 15 that faces the angled portion 9. The second bend 16 is bent in the offset direction 12. In other words, in the first end region 13 the tube body 2 is set back opposite the heat exchange portion 7 counter to the offset direction 12 due to the first bend 14. Accordingly, in the second end region 15 the tube body 2 is protruding from the heat exchange portion 7 and from the first end region 13 in the offset direction 12 due to the second bend 16. The bent portion 11, for example, has an S- or Z-like geometry 19. Between the first bend 14 and the second bend 16 a step bend 22 (see FIGS. 2A and 2B) can be present. The first bend 14 can have an S- or Z-like shape consisting of two sub-bends, one of which is directed against and one of which is directed in the offset direction, wherein both sub bends together cause the tube body 2 to withdraw counter to the offset direction 12 whilst distancing from the heat exchange portion 7 in the extension direction 8. When the first bend 14 comprises of two sub-bends, which both together have the S- or Z-like shape, the second bend 16 may steadily add to the S- or Z-like geometry as to form the S- or Z-like geometry 19 of the bent portion 11.

Additionally, FIGS. 1A, 1B, 2A and 2B show that the extension direction 8 substantially follows a straight line. The transverse direction 10 in the examples of FIGS. 1A, 1B, 2A and 2B is substantially perpendicular to the extension direction 8. It goes without saying that as an alternative the transverse direction 10 in contrast to the right angle of FIGS. 1A, 1B, 2A and 2B may be inclined by a different angle opposite the extension direction 8. The transverse direction 10 can follow a straight or a curved line. The distance D at which the angled portion 9 is arranged opposite the heat exchange portion 7 is smaller than a minimum bending radius R of the second bend 16. The minimum bending radius R of the second bend 16 for example is 3 to 6 times the tube thickness T of the tube body 2. The minimum bending radius R can be 0.70 to 0.95 times the tube width W. The minimum bending Radius R can be determined by an inner height H of the bent portion 11, which is measured along the offset direction 12. When progressively distancing from the heat exchange portion 7, the bent portion 11 firstly is set back counter to the offset direction 12 by the first bend 14, then the bent portion 11 by its second bend 16 begins rising in the offset direction 12 as to cross a plane containing the heat exchange portion 7 and lastly transfer into the angled portion 9 in the offset direction 10.

According to FIGS. 1A, 1B, 2A and 2B, the second bend 16 is a twist-bend 18. This means that in the second bend 16 the tube body 2 is bent and twisted at the same time, such that on the one hand the distance D between the angled portion 9 and the heat exchange portion 7 is bridged and on the other hand the exact same surface area of the tube body 2, which in the heat exchange portion 7 represents the top surface 4, mutates to the bottom surface 5 in the area of angled portion 9. Thus, the tube body 2 can be twisted 180° in the second bend 16.

As mentioned above, the flat tube 1 may be used in a heat exchanger 30 according to the invention. In FIG. 3A an example of the heat exchanger 30 according to the invention is partially depicted in a view against the transverse direction 10. The heat exchanger 30 has first flat tubes 1 according to the invention, one of which is illustrated separately in FIG. 3B in a view along the offset direction 12. Alternatively, the first flat tubes 1 of the heat exchanger 30 may accord to the examples of FIGS. 1A, 1B, 2A and 2B as described above. The first flat tubes 1 of the heat exchanger 30 each have a first longitudinal end 20 of their heat exchange portions 7, which faces away from their bent portions 11.

FIG. 4A shows the heat exchanger 30 in a plan view along the offset direction 12. As to be seen from FIGS. 3A and 4A, the first longitudinal ends 20 of the first flat tubes 1 are received in associated first openings 39 of a first collector 36 of the heat exchanger 30. Each of the first flat tubes 1 also has a second longitudinal end 21 of their angled portions 9, which faces away from their bent portion 11. These second longitudinal ends 21 are received in associated second openings 40 of a second collector 37 of the heat exchanger 30. The heat exchanger 30 furthermore has second flat tubes 31. These second flat tubes 31 have first longitudinal ends 32, which are received in associated third openings 41 of a third collector 38 of the heat exchanger 30. The second flat tubes 31 also have second longitudinal ends 33, which are arranged opposite their first longitudinal ends 32, which are received in associated fourth openings 42 of the first collector 36 of the heat exchanger 30. The first and the fourth openings 39 and 42 are arranged spaced apart from one another.

As to be seen from FIG. 3A, heat transfer fins 34 can be present at the outer top and bottom surface 4, 5, wherein the heat fins 34 protrude from the respective outer top and bottom surface 4, 5 along a fin height HF. The fin height HF is measured perpendicularly opposite the respective outer top and bottom surface 4, 5. The minimum bending radius R of the second bend 16 is 0.70 to 0.95 times the fin height HF.

According to FIGS. 3A and 4A, in the heat exchanger 30, the first flat tubes 1 and the second flat tubes 31 are arranged alternatingly along a stacking direction that corresponds to the offset direction 12 of the first flat tubes 1. For instance, this stacking direction equals the offset direction 12 of the first flat tubes 1. Between two adjacent flat tubes 1, 31 an intermediate space 35 can be present in the heat exchanger 30, in which the heat transfer fins 34 of the heat exchanger 30 are accommodated. In a view along the stacking direction the heat exchange portions 7 of the first flat tubes 1 for example completely overlap the second flat tubes 31, whereas the angled portions 9 of the first flat tubes 1 do at least partially not overlap the second flat tubes 31. For example, the second flat tubes 31 may substantially be straight. For instance, whilst assembling the heat exchanger 30, the heat transfer fins 34 can be held in place by the first bends 14 of the first flat tubes 1.

In an alternative example of the heat exchanger, which is—in a plan view along the offset direction 12—shown in FIG. 4B as an example, the second flat tubes 31 are configured to substantially accord to the flat tube 1 of the invention as exemplary depicted in FIGS. 1A, 1B, 2A and 2B and described above, wherein the transverse direction 10 of the first flat tubes 1 differs from the transverse direction 10′ of the second flat tubes 31. Thus, both the first and the second flat tubes 1 and 31 in the heat exchanger 30 may accord to the flat tube 1 according to the invention, wherein they are mounted in different, in particular mirrored, orientations in the heat exchanger 30. In the example of FIG. 4B, the first and the second flat tubes 1 and 31 are formed as identical parts, that only differ in their orientation in the heat exchanger 30.

While the above description constitutes the preferred embodiments of the present invention, the invention is susceptible to modification, variation and change without departing from the proper scope and fair meaning of the accompanying claims. 

What is claimed is:
 1. A flat tube (1) for a heat exchanger (30), comprising a tube body (2) delimiting at least one coolant channel (3) for a coolant or a refrigerant, the tube body having an outer top surface (4) and an outer bottom surface (5) arranged opposite one another at a thickness (T) of the tube body (2) and having two outer side surfaces (6) arranged opposite one another at a width (W) of the tube body (2), the outer side surfaces (6) connecting the outer top to the outer bottom (4, 5) surface, wherein the tube body (2) has a heat exchange portion (7) extending along an extension direction (8), wherein the tube body (2) has an angled portion (9) extending along an transverse direction (10) that is inclined with respect to the extension direction (8), wherein the tube body (2) has a bent portion (11) connecting the heat exchange portion (7) to the angled portion (9), wherein the angled portion (9) is arranged at a distance (D) from the heat exchange portion (7) measured in an offset direction (12) perpendicular to both the extension and the transverse direction (8, 10), wherein the bent portion (11) has a first end region (13) facing the heat exchange portion (7) with a first bend (14) counter to the offset direction (12), and a second end region (15) facing the angled portion (9) with a second bend (16) in the offset direction (12).
 2. The flat tube (1) according to claim 1, wherein the second bend (16) is a twist-bend (18).
 3. The flat tube (1) according to claim 1, wherein the extension direction (8) follows a straight line.
 4. The flat tube (1) according to claim 1, wherein the transverse direction (10) is perpendicular to the extension direction (8).
 5. The flat tube (1) according to claim 1, wherein the distance (D) at which the angled portion (9) is arranged opposite the heat exchange portion (7) is smaller than a minimum bending radius (R) of the second bend (16).
 6. The flat tube (1) according to claim 5, wherein the minimum bending radius (R) of the second bend (16) is 3 to 6 times the tube thickness (T).
 7. The flat tube (1) according to claim 1, wherein the tube body (2) delimits numerous coolant channels (3) arranged in a queue along the width (W) of the tube (1), wherein directly adjacent coolant channels (3) are separated by a division wall (17) extending along the thickness (T) of the tube body (2).
 8. The flat tube (1) according to claim 1, wherein the tube body (2) comprises a uniform metal material.
 9. The flat tube (1) according to claim 1, wherein the bent portion (11) in a view perpendicular both to the extension and to the offset direction (8, 12) has an S- or Z-like geometry (19).
 10. A heat exchanger (30), comprising: a first collector (36), a second collector (37), and a third collector (38); first flat tubes (1), each of which has a tube body (2) delimiting at least one coolant channel (3) for a coolant or a refrigerant, the tube body (2) having an outer top surface (4) and an outer bottom surface (5) arranged opposite one another at a thickness (T) of the tube body (2) and having two outer side surfaces (6) arranged opposite one another at a width (W) of the tube body (2), the outer side surfaces (6) connecting the outer top to the outer bottom (4, 5) surface, wherein the tube body (2) has a heat exchange portion (7) extending along an extension direction (8), wherein the tube body (2) has an angled portion (9) extending along an transverse direction (10) that is inclined with respect to the extension direction (8), wherein the tube body (2) has a bent portion (11) connecting the heat exchange portion (7) to the angled portion (9), wherein the angled portion (9) is arranged at a distance (D) from the heat exchange portion (7) measured in an offset direction (12) perpendicular to both the extension and the transverse direction (8, 10), wherein the bent portion (11) has a first end region (13) facing the heat exchange portion (7) with a first bend (14) counter to the offset direction (12), and a second end region (15) facing the angled portion (9) with a second bend (16) in the offset direction (12), wherein first longitudinal ends (20) of the heat exchange portions (7) facing away from the bent portions (11) are received in associated first openings (39) of the first collector (36) and second longitudinal ends (21) of the angled portions (9) facing away from the bent portions (11) are received in associated second openings (40) of the second collector (37); second flat tubes (31), wherein first longitudinal ends (32) of the second flat tubes (31) are received in associated third openings (41) of the third collector (38) and second longitudinal ends (33) of the second flat tubes (31), which are arranged opposite the first longitudinal ends (32), are received in associated fourth openings (42) of the first collector (36); wherein the first and fourth openings (39, 42) are arranged spaced apart from one another.
 11. The heat exchanger (30) according to claim 10, wherein the first flat tubes (1) and the second flat tubes (31) are arranged alternatingly along a stacking direction that corresponds to the offset direction (12) of the first flat tubes (1).
 12. The heat exchanger (30) according to claim 11, wherein in a view along the stacking direction, the heat exchange portions (7) of the first flat tubes (1) completely overlap the second flat tubes (31), whereas the angled portions (9) of the first flat tubes (1) do not.
 13. The heat exchanger (30) according to claim 10, wherein between adjacent flat tubes (1, 31) an intermediate space (35) is present, in which heat transfer fins (34) are accommodated.
 14. The heat exchanger (30) according to claim 10, wherein the second flat tubes (31) are straight.
 15. The heat exchanger (30) according to claim 10, wherein each of the second flat tubes (31) has a tube body (2) delimiting at least one coolant channel (3) for a coolant or a refrigerant, the tube body having an outer top surface (4) and an outer bottom surface (5) arranged opposite one another at a thickness (T) of the tube body (2) and having two outer side surfaces (6) arranged opposite one another at a width (W) of the tube body (2), the outer side surfaces (6) connecting the outer top to the outer bottom (4, 5) surface, wherein the tube body (2) has a heat exchange portion (7) extending along an extension direction (8), wherein the tube body (2) has an angled portion (9) extending along an transverse direction (10) that is inclined with respect to the extension direction (8), wherein the tube body (2) has a bent portion (11) connecting the heat exchange portion (7) to the angled portion (9), wherein the angled portion (9) is arranged at a distance (D) from the heat exchange portion (7) measured in an offset direction (12) perpendicular to both the extension and the transverse direction (8, 10), wherein the bent portion (11) has a first end region (13) facing the heat exchange portion (7) with a first bend (14) counter to the offset direction (12), and a second end region (15) facing the angled portion (9) with a second bend (16) in the offset direction (12), wherein the transverse direction (10) of the first flat tubes (1) differs from the transverse direction of the second flat tubes (31). 